This information is provided by
Provet for educational purposes only.
You should seek the advice of
your veterinarian if your pet is ill as only he or she can correctly advise
on the diagnosis and recommend the treatment that is most appropriate for
Note for Pet Owners:
Mycobacterium marinum can be
transmitted from fish and marine animals directly or indirectly through
water or contaminated equipment such as aquarium tanks and water-syphoning
tubes to humans. So, this infectious agent is a Zoonosis and protective
measures should be taken during handling to prevent transmission.
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Mycobacterium marinum is an organism that is commonly found in marine animals
The causative agent is an
acid-fast mycobacterium similar to the organism which causes tuberculosis in
It causes tuberculosis in fish and can cause
infection in humans and other species who come into contact with contaminated
water (eg from fish tanks) or marine animals.
The organism thrioves at high temperatures (77oC)
such as prevails in tropical aquaria.
All fish (freshwater and marine) are susceptible to
develop fish TB - especially the Anabantids, Characins and Cyprinids
In humans the disease occurs worldwide and it is
seen in individuals exposed through work or leisure activities to contaminated
water or marine animals. The incidence in the US is low, and reported to be
about 0.27 cases per 100,000 population per year. Transmission of the disease
has been reported following a bite from a dolphin.
In fish Mycobacterium marinum causes systemic
tuberculosis in ectothermic fish. This disease is characterised by granulomas
in internal organs. Other signs include :
- Weight loss (to emaciation)
- Bulbous eyes (exophthalmia)
- Skin defects
- Spinal deformities
- Distension of the abdomen
- Sudden death - sometimes occurs before other signs
In reptiles Mycobacterium marinum
infection has been reported to occur in the extremities of a collection of
ectothermic Egyptian spiny-tailed lizards, Uromastyx aegyptius. These animals
had been housed in a large, dry, but unsterilized tank previously used for
fish. They suffered from a progressively debilitating disease and symptomatic
treatment was unrewarding Histopathology of biopsy specimens was
necessary to diagnose this condition.
humans the disease rarely affects children :
- Usually causes localised infections following
access through traumatised skin.
- There are 2 main types of skin lesion, which most
often affect the hands :
- Single granuloma - appears as an erythematous
(pink-purple) nodule up to 3cm in diameter.
- Ascending lymphangitic granuloma - resulting
in multiple nodules, lymphadenopathy
- Less commonly : septic arthritis/osteomyelitis
with swelling of the joint
- Disseminated disease - rare, but seen occasionally
in immune-compromised patients, and results in death
Disseminated disease in immune-compromised patients
- Mycobacteria may be cultured
from the lesions (must be conducted at 32oC).
Takes 4-6 weeks
- Identification of acid-fast
mycobacteria can be made on histopathological examination of biopsies taken
from the nodules :
- Lesions less than 3
months old - acid fast bacilli in inflammatory tissue
- Lesions 6 months old -
acid fast bacilli in tuberculous granuloma
- PCR studies (polymerase chain
reaction) to identify organism
In fish - affected individuals should be destroyed and
removed form the tank. The infection will be transmitted if cannibalism occurs. NB
the human health risk if handling fish or cleansing tanks.
In humans :
- Antibiotics -need to be given for at least 2 months
duration. The following have been reported successful in the treatment of
human infection :
- Rifampin - adult humans - 600mg orally -
four doses/day. Can be given and is effective by itself.
- Minocycline - adult humans - 100mg orally twice
daily. Can be given, and is effective by itself, however resistant
strains of M.marinum have been reported to occur.
- Trimethoprim sulfamethoxazole combination -
160mg Trimethoprim/800 mg sulfamethoxazole orally every 12 hours for
- Ethambutol (needs to be given in combination
with another antibiotic eg rifampin) - 25mg/kg orally - four doses/day
The prognosis is poor for
infected fish, but good for most human patients